FIELD TESTING AND EVALUATION OF DUST DEPOSITION AND ...

5. DETERMINATION OF PARTICLE REMOVAL RATES,
EMISSION FACTORS, AND INJECTION HEIGHTS ON AN
UNPAVED ROAD IN AN ARID SETTING
As part of an ongoing DoD-funded contract, leveraged by this WESTAR project,
field experiments were performed at the Ft. Bliss military facility near El Paso TX.
Towers instrumented with particle monitors were used to measure the vertical
concentration profiles and horizontal flux of PM 10 dust particles emitted from an unpaved
road. These data provided both an estimate of emission factors for a number of vehicles
and an estimate of the fraction of PM 10 emissions that is regionally transportable. During
the same field campaign, the turbulence behind moving vehicles was examined because
of a hypothesis that the spatial extent of the wake may have a strong influence on the
transportable fraction of emitted dust particles. In this Chapter, the results of the Ft. Bliss
field tests are presented. Those results are compared with predictions from both the ADE
and the ISC models.
5.1 Methods
5.1.1 Upwind/Downwind Towers
From April 11 through 24, 2002 unpaved road emissions experiments were
conducted at Ft. Bliss. The procedure was based on an upwind/downwind technique that
has been used by other investigators (e.g., Gillies et al., 1999; Cowherd, 1999). Three
towers were set up collinearly and perpendicular to a 1,000 m section of unpaved road on
the open range of Ft. Bliss, TX, which was oriented in a north-south direction. Historical
meteorological data indicated that winds at this time of year in this area were
predominantly from the west.
The three towers were all downwind of the road at distances of 7 m, 50 m, and
100 m. The tower closest to the road was 6 m high with the other two being 12 m in
height(Figure 5-1). Each downwind tower was instrumented with four DustTraks (Model
8520, TSI Inc., St. Paul, MN) that were spaced logarithmically in the vertical direction.
The DustTrak is a portable, battery-operated, laser-photometer that uses light scattering
technology to determine mass concentration in real-time. In applied studies of dust
emissions from playa surfaces and partially vegetated surfaces Houser and Nickling
(2001), and Nickling et al. (1997), respectively, found these instruments to be superior to
the traditional method of collecting suspended sediment on filters. Etyemezian et al.
(submitted) and Kuhns et al. (2001; submitted) used DustTraks to measure PM 10
emission from paved and unpaved roadways using an on-board vehicle measurement
system.
The tower at 7 m downwind (DT_1) had measurement positions at 0.76, 1.28,
2.66, and 5.18 m above ground level (AGL). The second tower (DT_2) at 50 m had
measurement positions at 1.25, 2.6, 5.7, and 12.2 m. The third tower at 100 m (DT_3)
had the same measurement positions as DT_2 with an additional sampling location at 0.4
m. The DustTraks were equipped with PM 10 inlets and measured particle concentrations
at intervals of 1 second. Four anemometers, one wind vane, and one temperature probe
were mounted on the DT_3 tower in order to characterize the local meteorological
conditions. During the course of the study four GRIMM model 1.108 particle size
5-1